1. Field of the Invention
The invention relates to a truck mounted lift mechanism for loading and unloading containers. More particularly, the invention relates to a vertically movable lift mounted on a horizontally movable carriage carried by a truck for lifting and transporting containers.
2. State of the Art
The state of the art is well represented by U.S. Pat. No. 4,778,327 to Tufenkian et al. and by U.S. Pat. No. 4,943,203 to Bohata.
Tufenkian et al. disclose a bin lifting mechanism which is mounted on a flat bed truck for transporting waste product containers. The lifting mechanism includes a track extending along the length of the truck bed, a tray which can be moved along the length of the track and a jack-up assembly (fork lift) attached to and supported by the tray. A pair of hydraulic cylinders attached between the tray and the jack-up assembly permit forward tilting of the jack-up assembly toward the truck cab. In use, the tray carrying the jack-up assembly is moved to the rear of the truck. The fork is lowered below the truck bed and the truck is backed towards a container until the fork engages sleeves in the container. The fork is then raised, lifting the container above the truck bed. The tray is moved by hydraulic ram towards the truck cab and the jack-up assembly is tilted toward the cab. Tufenkian et al. thereby locate the container in a balanced location in the center of the truck bed so that the container can be safely transported.
Bohata discloses a similar arrangement but with the added ability to tilt the truck bed so that the fork can be brought closer to the ground. Bohata also teaches the use of rollers between the track and the tray whereas Tufenkian et al. only show the tray sliding on the track with skids.
Both of these arrangements are limited to handling loads of about 2,500 lbs. This is partly because neither provides any rear stabilization on the truck bed to prevent the rear wheels of the truck from acting as a fulcrum while the container is being lifted off the ground. Other load limiting factors include the absence of rollers or the type of rollers used between the tray and the track.
The prior art is also limited in the amount of horizontal movement available to the tray. In the prior art, hydraulic cylinders or a winch and cable are used to move the tray and these occupy space which cannot be traversed by the tray. Neither prior art arrangement is capable of reaching very far below the truck bed to lift a container out of a hole or located on a slope. Articulation of the fork of the prior art arrangements is limited to vertical movement and some forward or rearward tilting.